The present invention relates to a projection television set having a large size screen formed by joining a plurality of Fresnel lenses. Also, the present invention relates to a projection television set having a seamless screen which is to be projected from a plurality of projectors.
In general, a projection television set is provided within a body casing with a CRT unit, an LCD unit and a projector including a projection lens. The projector is provided with a single RGB unit. A screen assembled by a Fresnel lens and a lenticular sheet is provided in a front face of the projector.
Japanese Patent Application Laid-Open No. Hei-3-73938 discloses a projection television set in which four unity Fresnel lenses are joined together. A reinforcement sheet is used to support the Fresnel lenses with centers of the four Fresnel lenses being fixedly aligned with the reinforcement sheet.
Thus, it is unnecessary to perform a centering operation of the screen center in the former projection television set where a single Fresnel lens corresponds to a single RGB unit. In the latter case, the centering operation of the laterally arranged Fresnel lenses is performed through the reinforcement sheet. Therefore, the reinforcement sheet is needed, resulting in the increased number of the components and in degradation in brightness. In such a case, if the right and left centers would not be aligned well, a seam line of the joint line of the Fresnel lenses and the lenticular sheets would appear on the image, so that the quality of the image would be worse.
On the other hand, a conventional multi-unit projection television set P.sub.o has a structure as shown in FIG. 13 (Japanese Patent Application No. 2-402519). For instance, four projection television units 60 are piled up and down and right and left, so that screens 61, 61, . . . , 61 are formed on the front faces of the four projection television units 60. These screens are each composed of a lenticular sheet 63 and a Fresnel lens 64 which are overlapped on each other. Joints of the adjacent screens 61 are carried out as shown in FIG. 14. Namely, frames 65, 65 are mounted at edges of the overlapped Fresnel lenses 64 and the lenticular sheets 63 and are bonded together. Further, panel plates 67 are mounted on the frames 65. The panel plate 67 and the frames 65 are fixed together by screws 66 to thereby join the adjacent screens 61.
However, the above-described joint structure for screens suffers from a problem such that rays of light projected from adjacent projectors such as CRT units, LCD units and the like are shielded or interrupted by the panel plates 67 and will not reach the joint portions of the frames 65, as a result of which joint lines 62 are formed as shown in FIG. 15 and part of an image m is omitted.